Restructure integration files and Refactor test fixtures and helpers

[ykim-akamai]

📝 Description

• Restructure test directory layout to organize tests by CLI command (e.g., linodes, domains), with localized fixtures.py and helpers.py for each
• Remove duplicate test helpers and enhance exec_test_command with clearer error and debug messages
• Scope fixtures appropriately to improve test isolation and reuse
• Review and refine outdated or skipped tests for better reliability and coverage

✔️ How to Test

make test-int

📷 Preview

[ykim-akamai]

Note: Use # noqa: F401 when importing from local fixtures.py to suppress "imported but unused" warnings for fixtures required by test functions via pytest's fixture injection.

[ezilber-akamai]

This is a huge improvement! Looks good overall, but I got the following test failures locally:

FAILED tests/integration/linodes/test_linode_interfaces.py::test_interface_settings_update - RuntimeError: Command failed with exit code 2
FAILED tests/integration/regions/test_plugin_region_table.py::test_output - AssertionError: assert '-' in '│     │ IN  │     │     │     │    │     │    │    │     │     │    │     │    │'
FAILED tests/integration/ssh/test_plugin_ssh.py::test_ssh_instance_ready - TimeoutError: SSH timeout expired
ERROR tests/integration/linodes/test_backups.py::test_create_backup_with_backup_enabled - NameError: name 'DEFAULT_LINODE_TYPE' is not defined
ERROR tests/integration/linodes/test_linodes.py::test_create_linode_without_image_and_not_boot - NameError: name 'DEFAULT_LINODE_TYPE' is not defined

[ykim-akamai]

Green Build on latest commit - https://github.com/linode/linode-cli/actions/runs/15691407989

[yec-akamai]

Nice job refactoring the tests!

[ezilber-akamai]

Nice work!